CVE-2026-53243rseq: Fix using an uninitialized stack variable in rseq_exit_user_update()

Official description

In the Linux kernel, the following vulnerability has been resolved: rseq: Fix using an uninitialized stack variable in rseq_exit_user_update() There is an bug in which an uninitialized stack variable is used in rseq_exit_user_update() as reported by syzbot: BUG: KMSAN: kernel-infoleak in rseq_set_ids_get_csaddr include/linux/rseq_entry.h:502 [inline] The local variable: struct rseq_ids ids = { .cpu_id = task_cpu(t), .mm_cid = task_mm_cid(t), .node_id = cpu_to_node(ids.cpu_id), }; According to the C standard, the evaluation order of expressions in an initializer list is indeterminately sequenced. The compiler (Clang, in this KMSAN build) evaluates `cpu_to_node(ids.cpu_id)` *before* `ids.cpu_id` is initialized with `task_cpu(t)`. This is fixed by moving the assignment of ids.node_id outside the structure initialization.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/e12d20a63b61aaf9de4772effccf42cc9a003e58
• https://git.kernel.org/stable/c/6d99479799c69c3cb588fcda19c81d8f61d64ecd